Amitraz is a valuable veterinary product effective against strains of ticks resistant to other chemical classes of ixodicides. It also possesses sufficient persistence on hair and wool to control all stages of parasitic ticks. The unique expellent action of amitraz causes ticks to withdraw mouthparts rapidly from, and fall off, the host animal. Effective tick control in conjunction with effective ecto or endoparasiticidal control is highly desirable in the raising, breeding and housing of healthy agronomic and domestic animals. Amitraz is, unfortunately, chemically unstable in the presence of solvents having a reactive hydroxyl group such as alcohols, glycols, water and the like. This characteristic has limited the development of veterinary compositions containing amitraz, and especially those containing amitraz and at least one additional parasiticidal agent, due to the combination of the instability of amitraz in hydroxyl-group-containing solvents and the insolubility of many parasiticidal agents in non-hydroxyl-group-containing solvents.
A further complication to the formulation of amitraz-containing compositions for use with animals is the cosmetic acceptability and non-irritability of the formulation when applied to the animal. Obviously, an acceptable formulation must be sufficiently easy to apply, dry within a reasonable period of time without impairment of the animal's appearance, be gentle on the animal's coat, non-irritating to the animal's skin and maintain its effectiveness on the animal through normal activities of the animal, such as exposure to sun and water. It must also be able to be applied to the animal in a small enough volume so that it can be applied so as to avoid the animal licking the area of application. Most desirably, the composition will provide the active ingredients in a formulation which will have at least a sufficient duration of activity, so as to avoid the necessity of frequent reapplication during this period of time.
Therefore, it is an object of this invention to provide a topical, parasiticidal veterinary composition containing amitraz, and at least one additional parasiticidal compound, which is stable, and which allows sufficiently high concentrations of each of the active ingredients.
It is likewise an object of the invention to provide a composition which provides for at least a one-month interval between applications.
It is another object of the invention to provide a method for the prevention, treatment and control of ectoparasiticidal infection or infestation in an animal, particularly a homeothermic animal.
An additional feature of this invention is that the compositions provided offer improved efficacy over a broad spectrum of parasites for an extended period of time.
Other objects and features of the invention will be come more apparent from the detailed description set forth hereinbelow.